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# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
# MA 02110-1301, USA.
# This is a simple and fast ASN1 decoder without external libraries.
#
# In order to browse through the ASN1 structure you need only 3
# functions allowing you to navigate:
# asn1_node_root(...), asn1_node_next(...) and asn1_node_first_child(...)
#
####################### BEGIN ASN1 DECODER ############################
# Author: Jens Getreu, 8.11.2014
##### NAVIGATE
# The following 4 functions are all you need to parse an ASN1 structure
# gets the first ASN1 structure in der
def asn1_node_root(der):
return asn1_read_length(der,0)
# gets the next ASN1 structure following (ixs,ixf,ixl)
def asn1_node_next(der, (ixs,ixf,ixl)):
return asn1_read_length(der,ixl+1)
# opens the container (ixs,ixf,ixl) and returns the first ASN1 inside
def asn1_node_first_child(der, (ixs,ixf,ixl)):
if ord(der[ixs]) & 0x20 != 0x20:
raise ValueError('Error: can only open constructed types. '
+'Found type: 0x'+der[ixs].encode("hex"))
return asn1_read_length(der,ixf)
# is true if one ASN1 chunk is inside another chunk.
def asn1_node_is_child_of((ixs,ixf,ixl), (jxs,jxf,jxl)):
return ( (ixf <= jxs ) and (jxl <= ixl) ) or \
( (jxf <= ixs ) and (ixl <= jxl) )
##### END NAVIGATE
##### ACCESS PRIMITIVES
# get content and verify type byte
def asn1_get_value_of_type(der,(ixs,ixf,ixl),asn1_type):
asn1_type_table = {
'BOOLEAN': 0x01, 'INTEGER': 0x02,
'BIT STRING': 0x03, 'OCTET STRING': 0x04,
'NULL': 0x05, 'OBJECT IDENTIFIER': 0x06,
'SEQUENCE': 0x70, 'SET': 0x71,
'PrintableString': 0x13, 'IA5String': 0x16,
'UTCTime': 0x17, 'ENUMERATED': 0x0A,
'UTF8String': 0x0C, 'PrintableString': 0x13,
}
if asn1_type_table[asn1_type] != ord(der[ixs]):
raise ValueError('Error: Expected type was: '+
hex(asn1_type_table[asn1_type])+
' Found: 0x'+der[ixs].encode('hex'))
return der[ixf:ixl+1]
# get value
def asn1_get_value(der,(ixs,ixf,ixl)):
return der[ixf:ixl+1]
# get type+length+value
def asn1_get_all(der,(ixs,ixf,ixl)):
return der[ixs:ixl+1]
##### END ACCESS PRIMITIVES
##### HELPER FUNCTIONS
# converter
def bitstr_to_bytestr(bitstr):
if bitstr[0] != '\x00':
raise ValueError('Error: only 00 padded bitstr can be converted to bytestr!')
return bitstr[1:]
# converter
def bytestr_to_int(s):
# converts bytestring to integer
i = 0
for char in s:
i <<= 8
i |= ord(char)
return i
# ix points to the first byte of the asn1 structure
# Returns first byte pointer, first content byte pointer and last.
def asn1_read_length(der,ix):
first= ord(der[ix+1])
if (ord(der[ix+1]) & 0x80) == 0:
length = first
ix_first_content_byte = ix+2
ix_last_content_byte = ix_first_content_byte + length -1
else:
lengthbytes = first & 0x7F
length = bytestr_to_int(der[ix+2:ix+2+lengthbytes])
ix_first_content_byte = ix+2+lengthbytes
ix_last_content_byte = ix_first_content_byte + length -1
return (ix,ix_first_content_byte,ix_last_content_byte)
##### END HELPER FUNCTIONS
####################### END ASN1 DECODER ############################
def decode_OID(s):
s = map(ord, s)
r = []
r.append(s[0] / 40)
r.append(s[0] % 40)
k = 0
for i in s[1:]:
if i < 128:
r.append(i + 128*k)
k = 0
else:
k = (i - 128) + 128*k
return '.'.join(map(str, r))
def encode_OID(oid):
x = map(int, oid.split('.'))
s = chr(x[0]*40 + x[1])
for i in x[2:]:
ss = chr(i % 128)
while i > 128:
i = i / 128
ss = chr(128 + i % 128) + ss
s += ss
return s
def asn1_get_children(der, i):
nodes = []
ii = asn1_node_first_child(der,i)
nodes.append(ii)
while ii[2]<i[2]:
ii = asn1_node_next(der,ii)
nodes.append(ii)
return nodes
def asn1_get_sequence(s):
return map(lambda j: asn1_get_value(s, j), asn1_get_children(s, asn1_node_root(s)))
def asn1_get_dict(der, i):
p = {}
for ii in asn1_get_children(der, i):
for iii in asn1_get_children(der, ii):
iiii = asn1_node_first_child(der, iii)
oid = decode_OID(asn1_get_value_of_type(der, iiii, 'OBJECT IDENTIFIER'))
iiii = asn1_node_next(der, iiii)
value = asn1_get_value(der, iiii)
p[oid] = value
return p